Answer: Botryoid embryonal rhabdomyosarcoma

Histology: Much of this fragmented biopsy is histologically bland, and could pass for an inflammatory polyp in that the stroma is myxoid and the cells do not show cytologic atypia. However, in other areas of the biopsy there is condensation of primitive stromal cells beneath the epithelium, forming a so-called “cambium-layer.” These primitive cells have wisps of eosinophilic cytoplasm, and were immunoreactive for myogenin and desmin on immunostains.

Discussion: Polyp formations are often seen in patients with cystitis, particularly in association with a stent. Inflammatory myofibroblastic tumor (IMT) would not demonstrate immunoreactivity for Myogenin, and often labels for ALK. The cells of an IMT generally have more hypochromatic nuclei than those of a rhabdomyosarcoma. Eosinophilic cystitis may be seen in patients with allergic conditions; however, in most cases eosinophilic infiltration of the bladder is secondary to a prior biopsy. Eosinophilic cystitis would not show the spindle-cell proliferation seen in the current case. Botryoid embryonal rhabdomyosarcoma is associated with a favorable prognosis relative to other subtypes of rhabdomyosarcoma.